SUMMARY: The level of origin of digital branch to thumb (DBT) of
superficial branch of radial nerve (SBRN) and its relationship to
brachioradialis muscle tendon (BRT) and its fascial sheath (FS) were
studied on both sides of upper extremities of 50 cadavers (n=100). The
DBT of SBRN originated in the middle third of forearm in 3 cases (3%),
distal third of forearm in 10 cases (10%) and in wrist and dorsum of
hand in 87 cases (87%). All cases having origin in the middle third of
forearm and half of the cases having origin in the distal third of
forearm were closely related to BRT or its FS. The clinical importance
of the study lies in the fact that the DBT supplies dorsum of the thumb
and first web space which has least cutaneous overlapping. Any injury or
entrapment of this nerve may lead to painful neuritis. Anatomical
knowledge of such variations are important for neurologists and surgeons
performing operative procedures in Quervain's release, arthroscopy
and Wartenberg's disease.

Since 19th century, distribution of superficial branch radial nerve
(SBRN) has been well documented in classical anatomy textbooks and
surgical atlases. Some articles have reported great variability in the
branching pattern and its distribution but it is often taken for granted
that only few branches cross the wrist joint and innervate the skin of
the radial side of the dorsum of hand and three and half digits.

Utmost care must be taken not to damage the sensory branches of
radial nerve which run across the area towards the dorsum of the hand.
Despite a careful approach by majority of the surgeons, damage to these
branches may occur inadvertently. Paraesthesia, hypesthesia, and painful
neuromas may result due to excessive retraction, partial or complete
transection of nerve (Fritz De Quervain, 1895). There are number of
reports on the branches of SBRN passing through dorsum of hand (Leao,
1958).The overlapping pattern of SBRN with lateral antebrachial
cutaneous nerve have also been observed in past research studies
(Mackinnon & Dellon, 1985). The SBRN becomes subcutaneous as it
emerges from posterior border of brachioradialis. It is here that the
nerve is likely to get injured (Braidwood, 1975). The anomalous pattern
where brachioradialis tendon (BRT) is split into two slips, there ate
chances of SBRN getting compressed between the two slips of BRT during
ulnar deviation of wrist when the BRT is stretched maximum (Turkof,
1995). However isolated neuropathy of SBRN have been found to be
exceptionally rare (Wilson, 1940). It was confirmed by further studies
that sensory neuropathies were poorly described in current textbooks and
were often misdiagnosed.

Similar to isolated involvement of lateral cutaneous nerve of
thigh, which is also known as meralgia paraesthestica, the compression
of SBRN is known by the term cheiralgia paraesthetica. This condition is
sometimes referred to as Wartenberg's disease (Wartenberg, 1954).
This condition was reported to be less rare than was originally thought
of. It is second in frequency to meralgia paraesthetica among
mononeuropathies (Sprofkin, 1954). SBRN in relation to surgical injuries
and entrapment neuropathies have been described but there is paucity of
literature regarding the level of division of digital branch to thumb
DBT of SBRN. As this is the branch which supplies dorsum of the thumb
and first web space, the areas which have least cutaneous overlapping.
Any injury to this branch during various surgical incisions or
entrapment may lead to hypaesthesia, paraesthesia and debilitating
neuritis. The aim of the present study was to note the level of division
of DBT of SBRN and define its relationship to BRT and its fascial sheath
(FS).

MATERIAL AND METHOD

Fifty non randomized cadavers (one hundred upper extremities) were
selected for study without any known history of trauma of disease from
the Department of Anatomy, Maulana Azad Medical College New Delhi,
India. Amongst these, thirty five were male and fifteen were female.
Forearm, wrist, dorsum of hand and digits were dissected. The SBRN was
traced in forearm and DBT was exposed in the forearm, hand and digits to
see the level of branching and distribution. To observe the level of
branching, the forearm was divided into three parts by considering two
bony landmarks--lateral epicondyle of the humerus and the radial styloid
process. The BRT and FS was also dissected to observe its distal
attachment and relationship to DBT. Observations were carefully noted
and photograph was taken (Fig. 1).

[FIGURA 1 OMITIR]

RESULTS

Table I shows that the DBT of SBRN was originating in the middle
third of forearm in three cases (3%), out of which two belonged to the
right forearm of male cadaver and one belonged to the left forearm of
female cadaver (Fig. 1). The DBT of SBRN originated from the lower third
of forearm in ten cases (10%), of which in two male and two female
cadavers, it was a bilateral variation, while in two male cadavers this
anomalous branching pattern was found unilaterally in the right forearm.
Rest of the cases (87%) showed digital branches originating at or distal
to the level of wrist joint. It was bilateral in twenty nine male
cadavers and twelve female cadavers. This variation was unilateral in
four male cadavers in the left arm and one female cadaver in the right
arm. This finding had no significant relationship with sex or right of
left arm.

In the three cases in which DBT of SBRN was originating from the
middle third of forearm, one was passing through the BRT and the other
two cases the DBT of SBRN was related to FS of BRT whereas in the lower
third forearm, out of ten cases, five were related to FS and none of
them were passing through the BRT.

In all cases (100%) where DBT was coming out from the middle third
of forearm, the nerve was closely related to the BRT or its FS whereas
only 50% cases showed the same relationship where the nerve was coming
from distal third of forearm.

DISCUSSION

Surgical procedures are commonly performed over dorsum of hand and
wrist in De Quervain's and Wartenberg's diseases. Recently,
wrist arthroscopy has gained wide popularity and being used by surgeons
as diagnostic and therapeutic modalities in treatment of many pericarpal
and intercarpal disorders (Auerbach, 1994). The commonest procedure, De
Quervain's release in which transverse skin incision approximately
1-2 cm proximal to radial styloid process is given (Luchetti, 2004) and
in wrist arthroscopy in which 1-2 portal (between short thumb extensors
and radial wrist extensors) are used, of the SBRN or its digital branch
is likely get injured as it is just underneath the skin in adipose
tissue (Trail, 2004). The lesion of this nerve cause painful neuromas
thus transforming the clinical picture into a grave and functionally
debilitating situation (Luchetti).

As per classical textbook description, it has been described that
SBRN runs lateral to radial artery behind brachioradialis, leaves the
artery 7 cm proximal to wrist and passes deep to BRT. It then curves
around lateral side of radius and becomes subcutaneous by piercing deep
fascia. It then divides into tire branches of which first two supplies
dorsal side of thumb and first web space (Standring, 2005). In the
present study, SBRN followed its usual course and became subcutaneous by
piercing the deep fascia. DBT of SBRN was originating in the middle
third of forearm in 3 cases (3%) and in the distal third of forearm in
l0 cases (10%) which further subdivided into two branches to supply
thumb and first web space whereas in rest of the cases (87%) all the
digital branches were originating at or distal to the wrist joint.

In an earlier study, out of twenty cases, two cases (10%) SBRN
became subcutaneous by piercing the tendon of brachioradialis (Abrams et
al., 1992) whereas another study reported that only in 2% cases SBRN
passed through split tendon of brachioradialis (Turkof et al., 1994). To
the best of our knowledge not much work has been done on the DBT of SBRN
and its relationship to BRT or its FS. An interesting finding which was
observed in the present study was that all the cases where the digital
branch of SBRN was originating from the middle third, pierced either
through the BRT or were related to its FS, whereas only 50% cases showed
the relationship of the digital branch to the BRT or its FS when it was
arising from the distal third of the forearm.

SBRN becomes subcutaneous as it emerges from posterior border of
brachioradialis. It is here that the nerve is likely to get injured
(Braidwood). The forearm pronation which is associated with the ulnar
deviation of the wrist, the slips of brachioradialis tendon get
stretched maximum and there are chances of compression of SBRN as it is
being impinged between the two slips of brachioradialis tendon (Turkof,
1995). In the present study, 100% cases in which DBT of SBRN was
originating in the middle third of forearm and 50% cases originating in
the distal third of forearm were related either to BRT or its FS.